text:
What is the benefit of spoilerons compared to ailerons?
Some airplanes like the B-52 or the MU-2 use spoilerons instead of ailerons to control roll. What is the benefit of ailerons vs spoilerons and vice versa?

Your question would be even better (esp. for casual visitors) if you included images or links to help people distinguish spoilers and ailerons.

Note that many airliners uses both sploilerons and ailerons for roll control at low speed.

Two reasons often-cited for having spoilerons:

better roll control (especially during stall)
doesn't take up space for flaps

Because of their location, they don't need to take up space which could be used for flaps. For example, on the MU-2, the primary reason for using spoilerons was to allow for full-span flaps at the rear, lowering clean wing area while still having acceptable stall speeds in the takeoff/landing configurations (and therefore shorter landing distances). This is one of the reasons for it to takeoff from runways less than 3000 feet, while having a cruise speed of up to 300 knots.
However, spoilerons have the disadvantage of killing lift, which can be deadly in situations such as a one-engine-out situation in a twin. To compensate for this, usually minimal constant spoiler use is recommended, and mostly rudder is used if an engine fails. If available, aileron trim (despite the name, there aren't any "real" ailerons on such an aircraft) is used to reduce drag if long-term use is expected.
Spoilerons tend to have less of a difference in roll rates at low and high speeds, compared to ailerons -- this could either be considered an advantage or a disadvantage, depending on the situation and whether a pilot is used to one type of roll control or another. This can negatively affect the roll control feel of the aircraft though, as it might feel slightly sluggish at higher airspeeds. They also tend not to provide much (if any) feedback to the pilot, which is a disadvantage.
Note that most large airliners use both spoilerons and ailerons for roll control, to be able to still have an aileron while supplementing large control inputs with the spoilers.

Aside from freeing up trailing edge space for flaps, spoilerons induce no adverse yaw when they are deflected.
Ailerons can cause a yawing moment opposite the roll direction leading to uncoordinated flight; spoilerons, because they only deploy on the low wing, can in some installations result in proverse yaw that can serve to reduce the need for rudder coordination.


text:
If there is a misprint on an instrument plate, is a pilot required to comply with it?
This is a snippet from the KESC RNAV 36 approach.  It's a real procedure, I didn't photoshop it except to add highlighting.
Let's say I was in the position that the blue aircraft is in (roughly 10 miles from WOKOL bearing approximately 320), and I had been cleared to WOKOL for the RNAV 36. I am assuming ATC did not explicitly tell me to do a procedure turn.
What am I supposed to do when I get to WOKOL?  The plate says NoPT, which is obviously a mistake.  Do I still fly the course reversal?  Do I whip into a 150 degree left turn over WOKOL as illustrated?
Here are some relevant passages from the AIM:
AIM 5-4-9:

The procedure turn or hold-in-lieu-of-PT is a required maneuver when it is depicted on the approach chart, unless cleared by ATC for a straight-in approach. Additionally, the procedure turn or hold-in-lieu-of-PT is not permitted when the symbol “No PT” is depicted on the initial segment being used, when a RADAR VECTOR to the final approach course is provided, or when conducting a timed approach from a holding fix.

AIM 5-4-5 (D. 2. b.)

The published procedure will be annotated to indicate when the course
  reversal is not necessary when flying within a particular TAA area;
  e.g., “NoPT.” Otherwise, the pilot is expected to execute the course
  reversal under the provisions of 14 CFR Section 91.175. The pilot
  may elect to use the course reversal pattern when it is not required by the procedure, but must inform air traffic control and
  receive clearance to do so.

If an instrument plate contains errors, am I still required to comply with them?

I don't see anything wrong with this plate. You simply enter the hold via a teardrop entry, which is not a PT. So after passing WOKOL you fly for 1 minute and then make a right turn to intercept the WOKOL 184 radial (004 inbound).

@PhilippeLeybaert - NoPT also applies to hold-in-lieu-of-procedure-turn.  Reference AIM 5-4-9.

@Qantas94Heavy - Are you required to fly the hold or do you have the option to fly the hold with ATC permission?  Reference AIM 5-4-5 (D.2.b.)

If I interpret this plate correctly, NoPT only applies north of WOKOL. But I could be wrong. I'm still in training for my IR.

@PhilippeLeybaert - You're interpreting the plate correctly.  The point is that the plate is wrong. NoPT is supposed to be on the south side of WOKOL, the quadrant away from the airport, but it's not.  The question is, do you still obey the chart when the chart is misprinted?

Now I may very well say something very stupid, but I still don't see anything wrong here. A PT is a maneuver to perform a course reversal. It doesn't necessarily say it should be a course reversal to fly inbound. The way I see it here: if you come from the south and you overshoot WOKOL you're not allowed to use a PT to reverse course if you need to join the hold (because of the "NoPT"). South of WOKOL it's perfectly fine. If that sounds stupid, it probably is. I'm a IR newbie :-)

The other obvious mistake on the plate is in the text: "Rwy 36 Straight-in and Circling and Circling...."  (how many times are you supposed to circle?)

@abelenky No, that's correct: the second "circling" applies to Rwy 18.

@Pondlife:  Rules of Grammar (not avaiation) mandate that commas separate subordinate phrases.  Without the comma, the text has too many "circlings".  It should read: "Rwy 36 Straight-in and Circling, and Circling to Rwy 18, NA at night."

For those that think that the chart is right, see my answer below.  The Jeppesen chart has it the other way.

The first thing that you should do is check the NOTAM's for the airport (which of course, you should do before you leave on your flight).  Very often, these types of errors have been discovered by someone else and the FAA will have issued a NOTAM to let everyone know.  In this case there is no NOTAM, so we would have had no reason to suspect an issue before we took off.
The main point has already been made.  If you are airborne and there is any reason to suspect that something is wrong, ask ATC for clarification and move on.
If I encountered this situation and couldn't ask for clarification (ie. lost communication) then I would simply select a different approach and fly it.
For the record, the Jeppesen chart has it coded correctly:

Now, aside from the operational considerations, it is very important to notify the FAA when you find discrepancies like this so that they can be fixed.  Here is a quote from the Aeronautical Chart User's Guide:

REPORTING CHART DISCREPANCIES
Your experience as a pilot is valuable
  and your feedback is  important. We make every effort to display
  accurate information  on all FAA charts and publications, so we
  appreciate your input.  Please notify us concerning any requests for
  changes, or potential  discrepancies you see while using our charts
  and related products.
FAA, AeroNav Products
SSMC4 Sta. 4503
1305 East-West Highway
Silver Spring, MD 20910-3281
Telephone Toll-Free 1-800-626-3677
E-mail: 9-AMC-Aerochart@faa.gov
Mark the chart you are using with the suggested
  changes and  include an explanation of the discrepancy. Mail this
  corrected  chart to the address above and we will send you a
  replacement  right away. Suggestions concerning this guide are also
  welcome.

For the record, I have already emailed the plate with the suggested changes to the email address above (on 24 DEC 2013), and hopefully a NOTAM will be issued soon and an amended approach procedure will follow sometime after.

Update (09 JAN 2014)
I received the following response from the FAA:

Dear Louis:
Thank you for reporting the problem
...
Control Number 18335 has been assigned to this issue for tracking
  purposes.  This concern has been closed with the following Response:
Thank You for your inquiry. A P-NOTAM is being assigned to correct the discrepancy.
Regards,

Note that the NOTAM hasn't been issued as of yet.
Update 2 (17 JAN 2014)
New NOTAM issued to address the error on the instrument approach procedure:
!FDC 4/3036 ESC IAP DELTA COUNTY, ESCANABA, MI.
   RNAV (GPS) RWY 36, ORIG...
     CHANGE TAA TO READ FROM 274/30 CW 094/30 (NOPT) TO WOKOL
     (IF/IAF) AND FROM 094/30 CW 274/30 TO WOKOL (IF/IAF).
   THIS IS RNAV (GPS) RWY 36, ORIG-A.
   1401171859-PERM

Update 3 (06 MAR 2014):
New, corrected chart issued and the NOTAM was cancelled the next day.

Nice answer.  The only problem is that if I notify the FAA and they fix it, how am I going to confuse CFI-I candidates during the oral portion of the check?

Upvoted for both the excellent answer and the fact you reported it to the FAA!

The literal answer to your question about complying with the plate is also in AIM 5-4-9, right after the piece you quoted (my bold):

NOTE- The pilot may elect to use the procedure turn or
  hold-in-lieu-of-PT when it is not required by the procedure, but must
  first receive an amended clearance from ATC. If the pilot is uncertain
  whether the ATC clearance intends for a procedure turn to be conducted
  or to allow for a straight-in approach, the pilot must immediately
  request clarification from ATC (14 CFR Section 91.123).

In other words, any time you aren't sure or you suspect something is odd then you should just ask ATC.
On the other hand, if your question is about this specific procedure and whether the NoPT notation is (or even can be) correct or not, you might want to phrase your question in that way.

Other RNAV approaches have the NoPT labeled on the the side away from the runway. This one is probably a misprint. If you believe an approach is incorrect, you should ask ATC just to make sure. If you feel the need to differ from an approach as published, whether because of a misprint, weather, traffic, a whim, or an emergency, you should ask or inform ATC.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

sort: votes


text:
What are the rules regarding (HUD) Head-up displays, especially glasses type?
What are the relevant regulations regarding use of HUD displays in non-military aviation?
The specific application in mind would involve providing information to pilots of turboprop survey aircraft flying VFR at about 100m altitude so it's of benefit to have the pilots' focus on what's going on out the window.

You can read about some guidance from the FAA about HUD design in these two Advisory Circulars:
General electronic displays
Enhanced Flight Vision Systems
This handbook is a bit dated but covers certification.
It really depends on what exactly the HUD is supposed to do. Any pilot can bring a handheld GPS along, with the understanding that it is not an "official" navigation instrument. A HUD could be used in a similar way. There are a couple things to keep in mind:
If the HUD is to be used for real navigation or pilot reference, then certification will be an issue. The handbook above talks about this. The HUD would need to be certified just like any other instruments in the cockpit for that use. If a HUD is used for special situations, like low visibility landing, it must be certified in order to be used in those situations. Otherwise you are not allowed to do anything you could not do without the HUD.
Even if the HUD is not to be used for critical flight data, the HUD needs to comply with the FAR 25 sections 25.773 and 25.775, which talk about the windows in the cockpit. The HUD can't interfere with the normal visibility the pilot should have.

Excellent answer, thanks so much @fooot.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
How is the lift generated by a number of out-of-plane staggered wings calculated?
I want to calculate the lift generated by a number of out-of-plane staggered wings but I don't think a valid approach is to simply use superposition and add the sum of the lift of all the wing's in isolation.
I have heard of Munk's stagger theorem but am unsure of it's implications.
I think the implication of Munk's theorem is that there is a limit to the amount of downwash and thus lift that can be generated by staggered wings.
Lets do an example:
I can calculate the lift force generated by a single planar wing as:
$$L=\frac{1}{2}\rho V^2SC_L$$
Where $\rho$ is air density, $V$ is free-stream velocity and $C_L$ is the finite wing lift coefficient, which is a function of the wing geometry.
Now, if I have say 5 staggered wings, is this statement:
$$L=5\times\frac{1}{2}\rho V^2SC_L$$
valid?
Now I know that the pressure distributions over the different wings will interact wing each other, but my question assumes that the wings are separated sufficiently far away from each other that this effect is negligible. Or is this interaction of pressure distribution a result of the stagger theorem?
I will appreciate any light being shed on this subject.

It depends on the vertical distance between the wings. Munk's theorem only covers the effect of their horizontal distance (in flow direction) and says it doesn't matter (in inviscid flow).
Your statement is correct if this distance is infinitely high (and the atmosphere has constant density over altitude). Only then there is no interference between the separate wings and their combined lift is the sum of the lift of every isolated wing.
On the other end of the scale, all wings together will just have the lift of a single wing if they are not separated at all. This is trivially easy to prove, but not practical.
For distances between the two extremes, lifting line theory gives you a good answer when the distance is not small. Below that, viscous effects will start to dominate the picture, and if the wings are separated only by something similar to the wing's thickness, they will impede the flow between the wings, making the combination appear as one blunt object to the outer flow, with consequences like flow separation and the collapse of lift.
Once you move the wings apart by more than their chord length, you will get practical solutions where the wings will produce more lift than a single one and even have lower induced drag than a single wing creating the same lift force. However, a distance sufficient to make interference negligible will mean that the struts between the wings will become long and heavy, so their mass cannot be neglected. I would expect that there is an optimum of lift minus mass which is somewhere around a vertical distance of one to three chord lengths.
Unfortunately, literature on the topic is more concerned with reducing drag, so the closest I could find is a work by Ilan Kroo on non-planar lifting systems. Using the solutions for biplanes will not give an answer to your question, because every wing interfers with every other, so adding a fourth and fifth wing to a triplane will reduce the lift of the triplane, but will in sum increase lift.

math nitpick: infinitesimally is tiny (e.g., $dx$), I think you were looking for infinitely

@Federico: Thanks, corrected.

Munk's theorem describes that when moving streamwise direction staggered wings AND keeping the circulation distribution (so changing incidence) the induced drag is kept constant.
It is not saying anything about lift (although can be obtained from circulation) and other drag components. What you are describing can't be derived from Munk's theory.
The difficulty is that one lifting surface modifies the pressure field around itself, having another wing affected by that pressure field will modify the pressure field on both wings affecting each other.
That situation is a complex aerodynamic situation, and very likely (so far I don't know) there is not analytical solution. You will need to use semi-empirical models like this ESDU or a simple panel method calculation. But it is not straight forward to calculate lift.


text:
What is the typical space allocated to first class vs. economy class passengers?
I'd like to know the space allocated to a typical first class passenger compared to that allocated to a typical economy class passenger.
For example, from SeatGuru, I can get the pitch and width of the seats on a British Airways Boeing 747 (economy is "World Traveller"). But can that give me the actual space allocated? Also, the first class seat is an "open suite" - does that mean there's space beyond pitch and width? Anyone ever done this calculation (in square feet or square meters)?

This will be tough to answer. First, what exactly does "space" mean? Second, there will be big differences between airlines and aircraft: a Singapore Airlines A380 suite will be huge compared to 'first class' on a US domestic B737 flight. It's also debatable if this question is even on topic or if it would fit http://travel.stackexchange.com better, but that's a separate issue.

kind-a related: http://www.economist.com/blogs/gulliver/2014/12/inequality-planes

There is no "typical". First class is one of the big ways that airlines differentiate from their competitors.

Width and pitch give you the space that is allocated to you and your seat. First Class seats are more bulky than Economy seats, so the actually usable space is a smaller fraction than in Economy. I wonder how the square meters would convey more information; generally, in Economy you are boxed in by your neighbors, while in First you can outstretch without reaching the limits of the cabin space allocated to you.
The aisles are wider in First, but it will be hard to make a concrete claim on "your" part of the aisle. Cabin crew in First will be more tolerant of eccentric behavior, so your mileage varies. Also note that in First on wide-bodied Aircraft every seat will have direct access to the aisle, so you will not need to step over the feet of your neighbor.
You also get more space for your baggage (luggage). On narrow-bodied aircraft two people sit in First Class where six would sit in Economy, so you get three times more space in the overhead bins. On wide-bodied aircraft this difference is even more pronounced, count on having in First the space of 5 ore more Economy seats. The bins are smaller, though.
Also, the steward will take care of your coat in First, so your space requirement is reduced as compared to Economy.

Thanks. Maybe then the calculation I'm looking for is: the total space of a first class compartment (floor space, coat space, overhead space) divided by number of passengers, and the same for the economy compartment. So your answer helped me reframe the question.


text:
Will an airliner with a quieter cabin have a quieter cargo hold?
I am aware that this question is on the border of travel and aviation but nobody on the travel side of the fence seems to be able to answer it. Apologies if it is regarded as off-topic for this site.
The question and answers on Are cargo holds pressurised these days? provide some good info on pressure and temperature management in airliner cargo holds but none on noise management.
As part of the process of emigrating my wife and I will be taking our cats with us on an 11 hour flight. I have travelled the route regularly on both A380 and Boeing 747 services. My experience is that the passenger cabin of the A380 is significantly quieter.
Will the experience for the animals in the hold be similarly quieter, or is noise in the passenger cabin separately and specifically managed?

It depends on the lengthwise location, not just on the cabin vs. cargo hold. At the tip of the fuselage most noise is coming from the air flowing around the fuselage, while engine noise will dominate in the rear part.

Is one of those types of noise easier to insulate against? Or would this affect the type of noise not the intensity?

Engine noise has a dominant frequency (easier to insulate) from the rotation speed of the parts inside, but they change with throttle setting (not easier anymore). I would expect it is quieter ahead of the wing, but I do not know how much difference the insulation actually makes. But I expect the cargo hold to be a lot noisier (Business class passenger pay more and complain more if they feel mistreated).

The cargo hold will probably be quieter if the cabin is quieter, but there are multiple variables that can affect this. As Peter Kämpf commented, the noise source will depend on the position in the airplane. The two main sources of noise are the air moving past the airplane, and the engines. The two main noise concerns of manufacturers and operators are cabin noise and community noise.
Reducing the noise at the source is one option. Engines are the main sources of noise and receive special treatment to reduce noise as much as possible. This can reduce cabin noise and/or community noise, and should help both the passenger and cargo decks. Newer aircraft like the A380 will tend to have quieter engine installations than older aircraft like the 747-400.
In the case of the cabin, noise can also be controlled with insulation. Insulation in the cabin will help with both noise and temperature control. Both are less important in the cargo hold, but do have some importance since it is only separated from the passenger area by the floor. Cargo hold insulation will provide protection for structure from fire or accidental damage, and some degree of temperature protection. So it is possible that the cabin receives added protection from these features that the cargo area does not benefit from.

A third source of noise is that 10-month-old baby in 27E

@rbp Unfortunately the FAA doesn't really regulate that noise source.


text:
How much computing power is needed to keep commercial and military planes flying?
I've always wondered, what sort of computing power is needed to keep modern commercial and military planes in the air?
There are many systems of a modern commercial plane (e.g an Airbus A350), that would need to be automated and controlled by computer, one example that springs to mind is autopilot, another is flight instruments.
Similarly I'm assuming that there'd be many systems (e.g fly-by-wire) that need to be controlled by computer in a modern military jet (e.g F-22 Raptor).
What sort of computing power is needed to run commercial planes and military jets, and how do they compare to each other, and how does their computing power compare to the computing power of modern commercial CPU's? (Could my 2nd-gen Intel i7 CPU, with the appropriate hardware to make it into a PC, hypothetically be able to control all the automated systems on a modern commercial plane or military jet?)

Could your single i7 (4 core) processor run all the flight systems on board a modern aircraft, no. Just like your car, there are dozens or more processors running highly optimized, specialized code. There isn't a way to run all that on a single system, even if it is significantly faster than what is used in aircraft today.

While the i7 has a power of less than 100 GFLOPS (probably 70 for a 4 GHz i7), a powerful video adapter has a power of 500 GFLOPS. So the power in a desktop computer is not really in the CPU, but in the GPU (as the size of the fans tells us).

One big difference is your average CPU is build to do anything in the average while the GPU is build to do one kind of task very well also tge CPU must control the GPU, Disks and others devices

@mins Do avionics systems perform enough floating-point calculations that GFLOPS (billions of floating point operations per second) would be an appropriate measure of performance? I can absolutely see some use for floating-point in avionics, but I can also see plenty of applications where fixed-point or integer arithmetic would seem to make more sense.

@mins Sure, the bottom line is we are comparing apples with oranges and OP apples with peanuts =)

"CPU must control the GPU, Disks and others devices". No, see this common Intel architecture, all these tasks are done by the so-called "south bridge" of the chipset.

Even in very old computers, the CPU was not managing the hard disk; only the floppy disk, on PC not Mac, and it showed in term of lag when doing low level formatting. All mass storage systems have their own controller. The CPU wouldn't even know how to interpret the low level encoding of in the physical storage.

For commercial airliners: the computing power is set during development and certification of the type. The A320 was developed in the 1980s and still uses Intel 80186 and Motorola 68020 processors. Your i7 CPU would be able to run rings around anything on board of the average airliner.
But processing capacity is of secondary importance to airliners, safety and redundancy are in the limelight. Any processor capacity that can do the job is good enough, and is only the start of all the aspects that go into certifying an airliner including its systems.
Image source
Military planes are different, in that the requirements are more pressing and the accepted risks are higher. Yes modern fly-by-wire planes use digital systems, however when the F-16 first came out with a fly-by-wire control system, it was a quadruple redundant analog system, with a digital processing requirement of zero. These were upgraded to digital fly-by-wire in the block 40/42 upgrade in the early 90s, so again the fly-by-wire used pretty primitive processors by today's standards.
Generalising, the long development and certification/ready-for-mission time of aircraft systems means that any system on board uses processing power that is behind the latest-to-market specs.

Even Military aircraft are pretty primitive by today's standards based on the advancement of electronics technology.  I remember when the F-22 rolled out in 1997, LMACO had bragged that the the two Common Integrated Processors (CIP) in the jet had the computational power of four Cray Supercomputers at the time;  These days, the average home PC is superior in processing power.

@CarloFelicione ...and a lot of the time, we use that home PC to watch videos of kittens.

With a current processor power, Flight Management would be more than possible. The mathematical operations in an automatic flight control system are quite simple (matrix multiplication, some transfer functions, some filters) for a cpu of today’s standards.
The trick would be to have a robust operating system (real time maybe), and to handle the I/O within the time window required for the control.
This answer assumes GPS and INS data are fused in a separate device, and actuator commands are driven through servo actuators.
Especially In military aircraft, and also in commercial aircraft several high frequency filters need to be included into the controller, to decouple it from structural modes. This brings in more computational requirements, but would be easily handled by the processor, as long as the necessary data I/O does not choke the processor.

Flight code is generally not cleverly designed to be efficient, but rather clear and simple, so an optimization rewrite can save some CPU time. If you only have 1 processor, then you have no redundancy to worry about, no need to log faults or data redording since only one thing that can fail, only I/O needed would be directly from sensors and to controls/displays. Leaves you with only the core functions to process. This slims the processor load down by at least half. Get rid of partitioned OS, TAWS, synthetic vision, controls channel b, assume external sensors and controls never fail and maybe, just maybe, you (not me) could fly on a single multi core i7, for some peiod of time.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
How flat does a runway need to be?
I always assumed that big runways are flat (or more specifically straight: they might have a slight slope in either direction), but while watching some crosswind landing footage shot at Birmingham Airport I noticed that the runway looks really uneven, and based on the videos it looks like this hinders safe landing especially in adverse weather conditions.

How common are uneven runways like this?
Does an uneven runway make landings more difficult?
Is there any standard on how flat a runway needs to be?

This too discussed curves in a runway.

The photograph in the question is taken with a long telephoto lens, which makes the undulations on the runway look much more severe than they really are.

Given that the runway is over 3000m, those undulations don't look very big. I doubt they had much to do with the landings in the video.
It's hard to make something that long completely flat.  The FAA has advisory circulars for all sorts of stuff in and around an airport.  One does cover flatness.
Airport Design Advisory Circular  Page 77 has recommendations on gradients including:

Vertical curves for longitudinal grade changes are parabolic. The length
  of the vertical curve is a minimum of 300 feet (91 m) for each 1.0 percent of change. A vertical
  curve is not necessary when the grade change is less than 0.40 percent.

Unfortunately, I could not find measurements of the undulations at BHX online, and I'm not going to estimate it from that photo.  Would be nice to know how much above or below these particular recommendations it is.

Yeah, the perspective in the video makes that runway look a lot shorter than it actually is.

As an anecdotal answer to your first two questions, paved runways used by air carriers that have obviously noticeable vertical curves are a minority but not uncommon.
Unless they've redone the runway at Stansted, north of London, there's a significant hump in the middle. I used to operate through it at night in the early 1990s. As a bit of fun, we'd arrange legs so that a new first officer would have the leg into Stansted. On final at night the hump was not noticeable. However, when you touched down, the runway lights along the last half of the runway would disappear, at which point the captain would observe, "Hmm, not much runway left."
If you define a runway simply as a strip of land regularly used by aircraft, there's a whole lot of them that have vertical curves, and many with horizontal bends as well. It's gone now, but there used to be a strip at a lumber mill in North Fork, California, that had a 10-15 degree bend in the middle. McKenzie Bridge airfield just upriver from my home in Oregon has a steep incline on the east end.
Landings and takeoff on uneven runways are not significantly more complex than on straight runways. If the runway qualifies as an uphill/downhill runway, you generally takeoff downhill and land uphill. Touching down on the downside of a hump can make your landing feel a little softer than otherwise. Touching down on the upside of a hump makes it a little harder than otherwise.
Accommodating a horizontal curve is more challenging. It's worth remembering, though, that seaplanes often use a curved takeoff run.

What about taxi path.  are they not required to be smooth? last time I flied, I noticed the ride is bumpy while taxiing. Not sure if it is always like that. I don't fly a lot. I was wondering if this was due to uneven paths.

@Dreadedsemicolon Generally taxiways at air carrier airports are smooth. I'm not sure what the motion is that you describe as "bumpy", but a less than smooth ride can be caused by intermittent braking, running over embedded reflectors or lights defining the centerline, out-round-tires, and some aircraft seem to rock rhythmically at certain taxi speeds.

I see. it wasn't violent bumps, so the reasons you listed must be the cause behind this. thanks for the response, I appreciate it.

@Terry can you expand on why seaplanes use a curved take-off run?

@Turkeyphant Three reasons that I can think of offhand:  (1) the waterway you're operating from is curved, (2) you're operating off smooth water and have to first generate a wake and then run back over it to get up on the step, and (3) there is no straight path on the water long enough so you have to use a circular path. On Google Ear see Daniels Field-OR78. We used to use the small lake with the little island in the middle by circling the island to get off.

Based on ICAO ( doc9157 Aerodrome design manuel part1 runways), the standard of vertical and horizontal slope of runways is:

For Horizontal Slope

1-1.5% for code letter C,D,E,F
1-2% for code letter A and B
Except intersections of another runway/taxiway where slope can be falter

And for Vertical Slope
Slope between max. and min evaluation of the runway centre line should be :

Code number 4: overall <1%,  1st and 4th quarter <0.8%, the other half <1.25%
Code number 3: overall <1%,  1st and 4th quarter <0.8%, the other half <1.25%
Code number 1/2: overall <2%

For slope change between 2 consecutive slope should be:

<1.5% for code number 3/4
<2% for code number 1/2

And for transition from one slope to another should be:

<0.1% per 30m code number 4
<0.2% per 30m code number 3
<0.4% per 30m code number 1/2

This is the global standard, some aviation authority such as FAA my have stricter rules


text:
Is there some technology which will help in stall recovery?
Although rare, it seems that there has been a number of cases where airliners have crashed as a result of a high altitude stall. I tend to picture this as entailing a long, uncontrolled descent where the plane never has proper flow over control surfaces to re-establish flight.
Is there any type of deployable technology that could force a plane into an attitude from which it could re-establish control? I am thinking of something like a drogue system that would force the nose down and dampen spin that could be jettisoned later.

I most of those cases the planes in fact did have proper flow over control surfaces, but pilots failed to apply correct recovery procedures.

Related questions: this, this and this.

elevators work pretty well

The only technologies needed:  Eyeballs, brain, hand, and stick. (maybe a little rudder).

Along the lines of what Peter said, yokes work very well for recovering from stalls. Throttles/thrust levers are also helpful.

On modern airliners we have audible stall warnings (ranging in complexity from a blaring horn to a voice saying "STALL. STALL. STALL."), stick shakers, stick pushers, and in some aircraft sophisticated flight envelope protection systems (control software that simply won't allow the pilot to stall the aircraft).
When everything is working as designed these systems either make it very difficult to stall an aircraft (you would have to ignore the audible warning, ignore the stick shaker, and either override or overpower the stick pusher), or impossible to do so (flight-envelope protection).
When things are not working as designed - e.g. if the pitot (airspeed) and angle-of-attack systems malfunction these protective systems can become ineffective, however in such a scenario any other automated protection system that we would seek to implement would have similar challenges to overcome (if the flight-envelope protection system can't determine that the aircraft is in a stall how would the hypothetical "stall recovery" system know that it should do its thing?)

The idea of airframe parachutes - even a "spin recovery drogue" - for airliners has its own problems and is a largely impractical solution. (I won't rehash the reasons here, but they are well covered in the linked question.)

"(if the flight-envelope protection system can't determine that the aircraft is in a stall how would the hypothetical "stall recovery" system know that it should do its thing?)" The scenario I was thinking of would be one where a pilot would make that decision.  Of course, that would assume that, at some time during a long uncontrolled descent, the pilot would realize they are in a stall but could not find the means to get out of it.  Your link was interesting but does not seem to apply to a system that would only be for changing the angle of attack, not slowing the descent.

From my (limited) experience in human/machine interactions, I think a stick pusher is a BAD idea.  When situations start to go badly, people get combative.  They view the situation as "me vs. the machine".  If the machine is pushing the stick forward, they try to pull the stick back.  Which is, of course, the wrong response.

@RobertHolton We already have a system which changes the angle of attack (the stick pusher literally pushes the stick forward, reducing the angle of attack). A parachute system would have to be triggered by the same logic (and there have been cases where stick pushers triggered when they really shouldn't have -- would you want a parachute deploying at the wrong moment in flight?) -- If we remove the computer from the equation and have the pilot decide when to pull the chute we're back in at "The pilot has to recognize the problem is a stall", at which point they don't need the chute…

@abelenky: Airplane won't stall unless the pilot is pulling on the control column due to longitudinal stability, so the stick pusher just increases force that is already there and that the pilot should already consider a sign of loosing speed. But as the accidents show, when the pilots both lost situational awareness, the machine is not able to wake them up whatever it does.

The real problem is complacency and over-reliance on technology. There is no technological fix for that.
Pilots have been made to believe that their computerized FCS will make stall impossible. When the system switches modes and the pilots do not become aware of this, they have in very few cases actively kept the aircraft in a stall, thinking they wouldn't stall, ever.
What is needed is better pilot training, and maybe less exposure to the propaganda from the aircraft manufacturers. Trusting the life of 300 people to a person who has never flown upside down, not to mention at bank angles of more than 60°, is reckless. In their race to ever lower cost the MBA types who run airlines today compare pilots to coach drivers and put as much effort in their education.

With the demise of large air forces in large wars, it is probably doubtful that as many people as once did will ever get the experience in flying a large aircraft close to the edge as combat pilots have.

@RobertHolton: It does not have to be a large aircraft. The point is to experience the sensory illusions, the reversed response to roll in inverted flight and learn to regain orientation in unusual attitudes. Which can be safely done in a higher-performance trainer, something like PC-9 or PC-21.

@JanHudec: Or a Zlin 226, at least in my case. Missing power can be replaced by kinetic energy if you tolerate longer climb sections in your training.

@PeterKämpf Can you expand on why experience in inverted flight is helpful for flying an airliner? I'm not trying to be sarcastic; I'm just legitimately curious what the benefits there are, having never personally flown inverted.

@reirab: It is less about flying inverted, but getting into and out of unusual attitudes. I could as well say they need to spin - not one turn, but at least 3 or 5. It opens your mind and prepares you for unexpected situations. You know what to expect and what to do next.


text:
Did CNN correctly state that AirAsia flight stalled and crashed?
CNN reported that the cause the crash of AirAsia Flight 8501 is:

... it stalled and fell out of the sky ...

The reality is that when an airplane stalls it does not fall out of the sky. Why did CNN report such a statement?
The aircraft was at 36,000 feet when it stalled. According to the flight recorder, it was descending at 6000 feet per minute. Stalling an airplane at 36,000 feet means there is plenty of time to recover from any stall, unless the airplane was loaded tail heavy. But that was not reported.
Am I missing something here?

A stalled aircraft is literally falling out of the sky, so that is correct. Whether it's recoverable or not depends on very many factors. In the case of AF447 one of those factors is realizing you're in a stall.

It is possible to be stalled such that you cannot get enough airflow over the elevators (or whatever other control surface is responsible for pitch) to recover from the stall.  Read about "deep stalls"

Regarding the title, no, they did not correctly report that is stalled, because that information is not confirmed yet. It was said by Indonesian Minister of Transport, so it might be the best founded speculation we have so far, but until NTSC confirms it, it is still a speculation. You can watch AvHerald coverage of the accident for any new reliable information.

Of course it follows that when we don't yet even know for sure whether the aircraft stalled, we can't really have a clue about why it did and why the pilots didn't recover it.

Whatever is said regarding 8501 is speculation since only a factual preliminary report has been released.  Therefore, this question is speculative, since we do not know that 8501 was stalled, nor that it "fell out of the sky" and I am voting to close as such.

Well, it seems likely that the plane stalled, and the plane didn't seem to leave the sky in a controlled way. So, yes, the plane stalled and fell out of the sky.

@DavidRicherby How do you know that it stalled?  How do you know that it didn't "leave the skit" in a controlled way? Are you privy to some facts which have not been made public?

@Simon You seem to have missed the part where I said "it seems likely that" and "didn't seem to". (Also, the asker seems to have missed the point where the linked CNN transcript has an interviewee saying the plain could have stalled and fallen out of the sky.)

@DavidRicherby I didn't miss anything.  I responded to your statement So, yes, the plane stalled and fell out of the sky.  It is not possible to make any statement yet other than it crashed, and people died.

An aerodynamic stall is exactly that: the wing is stalled and is not generating enough lift to keep the aircraft in the sky. The aircraft is falling out of the sky. Whether the stall can be recovered from, and therefore the aircraft can stop falling out of the sky, is an entirely different question.
Some stalls can be recovered from, others cannot... particularly if whatever caused the stall is preventing recovery.

An aerodynamic surface which is stalled is no longer generating significant lift. Most specifically it's not generating enough lift to support the aircraft
An object which is not generating sufficient lift to keep it airborne, and is being pulled towards the earth by gravity, is falling

So yes, CNN is correct - the plane fell out of the sky while stalled. Generally a plane which is at 36,000 ft and is not falling out of the sky, doesn't hit the ground.
As Falstro mentioned in his comment, AF447 didn't realise it was in a stall at all, so therefore couldn't remove it. We don't really have enough information about the AirAsia flight to be sure what happened

Stalled wing is definitely still generating lift. It is not generating as much of it, but it is generating some.

You're splitting hairs, the point is that it's not generating anywhere close to enough to prevent the aircraft falling out of the sky. Whether it's in a complete free fall or whether the fall is in any way arrested, is academic

in other words, it's not flying and it's not gliding

@JanHudec: Yes, you can fly in conditions where the wings are in a stall but is still generating enough lift to keep the aircraft aloft (we see this sometimes in aerobatic flying). But a stalled "aircraft" is defined as an aircraft where the wings are stalled to the point of not generating enough lift to counter the force of gravity. That's why when planes crash we say the aircraft stalled rather than just the wings.

Again splitting hairs in the context of this question. It wasn't an aerobatic aircraft and considering it dropped a wing and crashed into a river, it didn't appear to be marginal....

@JonStory Wrong flight. The Air Asia flight crashed from cruise altitude. The one that dropped a wing and crashed into a river was in Taiwan and had an engine failure shortly after takeoff.


text:
How does air enter and leave the cabin of an airliner?
Yesterday I flew on Airbus A320 and on the airline's board catalogue, there were written some "curiosities". On was written that the air coming from the air conditioning inside the fuselage is very dry, (3-10% humidity) because while it's warmed up from the freezing outside air, it is much more complicated to humidify it.
Firstly I never even thought that our breathable air comes from the outside.
Questions:

During flight, from where air intake is made in an aircraft?
Does this air also contain CO2 along with Oxygen dumped directly to the fuselage?

As an aside it is much cheaper to heat low humidity air. The air is just coming from the outside (indirectly through the engine which provides high pressure air), so there is no need to modify the $O_2$, $CO_2$ content.

@Th3alchemist the air always contain some amount of CO2 and larger amount of O2 wherever you go. It is outside air, not from special tank.

Ok thanks for clarifying that. Sorry the duplicate post.


text:
What training is required to become an air traffic controller?
I'm curious as to what it takes to be an Air Traffic Controller. I sat in a preliminary online test after I got accepted in, but it was mindbogglingly difficult. One of the questions I had to do was to add two 8-digit numbers in less then 5 seconds. With such difficult questions in mind, there must be on the job training in addition to class room training as well.
Q: What sort of training is done in becoming an ATC, and what sets the difference between a good ATC and an average ATC?

I don't know what goes on in a center, but in the towers they work really hard and have to do multiple things at once and be extremely vigilant at the same time. It's a hard job that requires a lot of intelligence.

Are you in the US? Are you interested in answers about other countries?

@relaxed I am in Sydney, but I think the standard of what they teach would be somewhat similar (apart from the laws and regulations)

In a word: attitude

@digitgopher I would have used discipline.

Do I hear a vote for "masochism"? :-)

Training for US path is(I'll take this information, post hiring, since they keep changing how they hire, and assign facilities, also length of times are approximate and might vary):
FAA Academy(Oklahoma City, OK):

~6 week AT Basics Course(If you went to a CTI(College Training Initiative) school, this course is skipped)
Then if you're split depending on which area you're going to, Enroute, Tower, or TRACON.
Tower course is ~8 weeks,  TRACON course is 1 month (or 2 if you're going to a bigger facility and they put you in a supplemental course), and Enroute, I'm not positive is around 10 weeks or so.

Then you move to your facility. At your facility, your first days you'll spend learning various materials, and then be given classroom training, including Computer based instruction, an actual instructor time(if the facility is large enough), and also lots of study time to memorize all the maps, and various items you will be tested on. Then, if your facility has the ability, you'll do some simulator problems. Note: you might only get the classroom and simulator for only a subset of positions at the facility, depending on how they break up the training.
Then after all that, you head out to the operation, and will usually start training on some subset of positions that are at the facility. You'll receive training on each position, until you've demonstrated that you're competent to work it on your own. Once/if you get to that point, you're given a certification check by your supervisor, and if you pass you're certified to work that position. And you repeat that process for each position, and possibly having to return to classrooms/simulators for any additional positions, and repeating the process again. Once you've finished all the positions you need you're a fully certified controller at that facility.
Each time you move to a new facility, you will have to repeat the classroom and simulator, and on the job training at the positions at that new facility.
There's far more detail and nuance than I can easily explain here, but this is a general overview of the process.

As far as timeline once you arrive at a facility...could take less than a year to become fully certified at a smaller tower; at a center could be closer to 3 years of on-the-job training.

The test you took was probably the AT-SAT (Air Traffic Standardized Aptitude Test).
Based on those results (and assuming you didn't completely blow it) you'll be sorted and assigned to a class at the FAA Academy for classroom and simulator training.
When you're proficient in the simulator and have completed the required classroom instruction you'll be assigned to a facility for training as a "developmental controller". You will shadow a fully certified controller, and eventually work live traffic under their supervision while learning local procedures and how the airspace system works in the real world (as opposed to the simulators you trained in).
Eventually you will have completed the local training required and demonstrated your ability to work traffic to your supervisor, and you will be certified as a "full performance level" controller.

As for what it takes to be a good controller, the standard answer is "If you would make a good waiter (or waitress) you will probably be a good controller."
The ability to see and anticipate a situation developing and take appropriate actions is probably the most vital skill (for wait staff it's making sure everyone's glass is full, for controllers it's making sure traffic is sequenced in a way that keeps things moving along in a safe, orderly, and efficient manner).
Beyond that it's hard to really say what makes a "good" controller, because everyone is looking for something different. (A "good" controller for a pilot gives them the clearances they want, when they want them. A "good" controller for the system occasionally gives a pilot a less-than-optimal routing or a delay vector in order to keep some other part of the system with more traffic volume moving smoothly.)

The AT-SAT may have some interesting content, but there is definitely no adding of 8 digit numbers for time!

@digitgopher I didn't recall that being in the practice test banks either - but if it wasn't the AT-SAT I'm not sure what it could have been (?)

I'd also add in that you need decent spatial intelligence.  Its one thing to see a problem develop, its another thing to understand how to convert the 2D display into a 3D solution.

@SHAF Indeed, the waiter analogy sort-of works here too (knowing what table bits to rearrange to get everything to fit) - although those problems tend to be two-dimensional :)

I dont know about paper and classroom training but they do train in the tower at KPNE where I fly. I know this because they sometimes tell you if they are training a new guy. This happened to me just the other night. I was flying in the pattern with my instructor (practicing night landings) and we were the only people around that evening. The tower told us they had a trainee in and we were good practice for them (they even asked us to stay out longer). They had him take us through both left and right traffic patterns and do a few leg extensions and what not. Nothing to out of the norm. I think one other plane came in while we were in the pattern but nothing that he could not handle.
My guess is that they start people at smaller towered airports, if you become senior enough/good enough to move to a bigger one you step up like in any other job. I would think they don't train guys at major airports but I cant state that as an actual fact.

Most of the answers are based on the US system, so let me give a very brief explination of how ATC training generally works in Europe.
Overall, you will not get accepted into the training programme unless there is a job for you in the other end. This means that the selection rounds prior to starting training is not just a matter of being fit for training - it also includes a job interview.
Many European countries make use of the First European Air Traffic Controller Selection Test (FEAST), which is a standardized, computer-based test used to evaluate potential ATCO trainees.
FEAST is used to assess your cognitive and mental skills such as IQ, working under time pressure, multi-tasking, logical planning, mathematics etc. etc.
If you pass the FEAST tests (there are two of them), you will be invited to the job interview, which is a pretty standard interview. Following the interview, if you are among the few lucky ones, you will have to undergo a medical examination and security clearance.
If you make it this far, you can start the actual education.
Training to become an ATCO takes about 3 years. The first half is part class-room, part simulator training, focusing on the huge amount of theoretical material you have to know as an air traffic controller. You will find many topics resemble those of pilot training: air law, radio communication, human factors and performance etc., but there are also more technical classes that deal directly with air traffic management.
The second half of the education consists of on-the-job-training (OJT). During this period, you will handle real air traffic in a real environment, under the supervision of an instructor, who will brief, de-brief and generally assist you. You will learn to apply your theoretical knowledge in practise, and get familiar with the airspace and local procedures of the facility where you will end up working.
Of course, during both the first and second half of education, you will have to take tests and exams to ensure you are keeping up with the goals and requirements.
Then finally, after about three years, you will walk into your familiar training facility, but the instructor will be gone, and you just get on with it . . .


text:
What distinct challenges are faced in taxi operations that aren't found in other phases of flight?
The Federal Aviation Administration (FAA) made Runway Incursion Avoidance a special emphasis area and added it as a required task in several of the Practical Test Standards (PTS) documents. All the PTS documents have a bullet item that reads something like this:

Distinct challenges and requirements during taxi operations not found in other phases of flight operations.

I have reviewed the applicable sections of the Pilot's Handbook of Aeronautical Knowledge and AC 91-73B, but I haven't found a concrete answer on what exactly these challenges are. If an examiner asked me to explain these challenges I'd do my best, and I'm sure I could come up with some good arguments for my thoughts, but I like to know what the FAA is looking for when they ask a question and this one doesn't seem to have an exact reference.

Look at the airport diagrams section in the AIM. Know what is a taxiway direction sign. What way you have to go to get on taxi ways and runways. What are hot spots and danger areas etc.  read the chart supplement for Chicago ohare to get a view of some things. Use it as an example if needed. But don't dig yourself a hole for the check ride.

Maybe this would be more appropriate as a wiki because it is so comprehensive.

Look at AC 120-74 (Procedures during taxi operations) which states "Taxi operations present distinct challenges and requirements not found in other phases of flight operations." If this is not that they have in mind...

Taxiing hazard #346:'t those pesky regional jets

Well, it's rare for a troop of monkeys to run in front of the aircraft at 30,000 ft, that's far more common when taxiing... admittedly dependant on your geography

Well in air you don't have to worry about kangaroos in your path or a wheel falling off unnoticed, or people beside a taxiway mistakenly indicating you won't hit a golf cart.  Heaven forbid you accidentally retract the landing gear.
Jokes aisde, taxiing can be a major challenge even for experienced pilots. First off, your traditional warning systems don't work.  You can't check your route using a low or mid-range GPS because they don't have airport taxiway information.  You won't get a "terrain!" warning when you're about to head off the end of a taxiway.
Steering is difficult because the control surfaces are used differently on the ground, especially in a crosswind.  You don't use your ailerons or elevator to control your path; you use them to keep the wings from lifting and to keep you on the ground.  You use the rudder and steerable nose wheel/tail-wheel (if present) to keep you on the right path, with help from the brakes only when necessary.   Those brakes definitely will be necessary in a tail-wheel aircraft with a strong enough crosswind.  If you fail to control the ground path in a tail-wheel aircraft, an unstable and difficult ground loop can develop.
Did wbeard52 mention low visibility? You can technically land a plane in zero visibility if your plane and the airport are properly equipped, but good luck naviagting the taxiways afterwards. A pilot once remarked that "Taxiing at ORD the first time in low visibility conditions is impossible," and another remarked that he was so confused by low visibility he had to have a follow-me truck guide him. [source]
Taxiing can also be confusing in good weather, especially at night.  Sometimes the taxiway letters jump randomly around the alphabet, sometimes markings are obstructed, sometimes there's construction (you don't see construction much in the air!).   The FAA has an entire handbook appendix devoted to avoiding runway incursions that explains these navigational issues.
You also have to be vigilant for obstacles around you (like those kangaroos I mentioned earlier).  In a tail-wheel aircraft with a high nose, for example, it's recommended to zig-zag a little so you can see what's right in front of you.   In aircraft like the B777-300 they actually have camera systems to augment visibility.  (see this question and the FAA's Airplane Flying Handbook ).
You can also look up a list of recent taxiing incidents here

There are quite a few challenges:

Low visibility taxi
Did I mention complex taxi routes in low visibility
Hot spots (which are designed to alert pilots to possible taxi operational challenges
Runway incursion
Winds and the possibility of the upwind wing rising unless compensated for.
Taxiing with your feet and staying on the yellow line
Jet blast
Taxiing on a snow covered or icy taxiway

Challenges:

Your airplane is on ground, so the physics of ground play role. Slipping, skidding, stopping, decelerating, pushback etc.
Visual outlook responsibility is both the pilot's and the tower's and any other traffic's.
A fuel truck or passenger bus or a follow me car can hit you any time.
Navigating on the airport can be stressful for a first comer pilot, especially if it's a crowded airport.

Whereas in air, most of the events are foreseen, and the autopilot handles most of the detailed tasks and creates the situational awareness to give time for the pilot to think carefully.


text:
If jets carried pure O2 to use for combustion, would they be more efficient?
Air is around 21% Oxygen. The bulk of air is non-flammable Nitrogen. Wouldn't surrounding the jet fuel with only O2 create more efficient and clean combustion?

Vehicles which carry their oxidizer with them are called rockets. It is a good thing that air is not pure $O_2$, because the nitrogen, being employed as a process gas,  helps to get useful work from the combustion process. By being heated and accelerated in the combustor, it does the main work of driving the turbine and turning heat into mechanical work. Engines would be even cleaner if less oxygen is around, because already at 21% $O_2$ they run at fuel-to-air ratios well below the stoichiometric optimum.
If you consider the amount of air flowing through the core of a modern turbofan, you will see that the amount of oxygen which needs to be available will dwarf the amount of fuel, and most of it would not burn but would replace nitrogen in its role as the process gas. It could not be carried with the airplane nor isolated from surrounding air if any meaningful payload and range should remain.
For some background on the combustion process, please see this answer.

Would high bypass turbofans or turbojets be more happy to breathe pure oxygen?

For the same reason, some drivers in some races where the rules allow for have nitrogen boosters for their cars.

@ChristianHujer: Isn't this nitrous oxide, a compound of nitrogen and oxygen? It helps to boost performance when injected into the intake air of piston engines, because it contains more oxygen per gram than air and is a metastable compound, so its dissociation at 600°C sets free some more energy. Piston engines are different animals than jets; they profit from having oxygen-enriched air.

@shortstheory: No, they would run too hot. Please read the answer to this question for more details.

@PeterKämpf Oh, you're right, I'm wrong. Thanks for pointing it out, and I just learned something new.

Nitric oxide formation is in fact one of the reasons why 21% O2 is actually too high. At 2000K, leftover oxygen which doesn't react with the fuel will instead react with nitrogen to produce NO and NO2.

@MSalters ... like it does in Diesel engines, regardless of what Volkswagen is telling us.

Then the weight of the oxidizer would weight down the aircraft. For each kilogram of pure octane (one of the components of jet fuel) you would need around 1.7 kilogram of pure O2. In other words it would double the weight of the fuel you have to bring.
Also bringing your own oxidizer is what happens with rockets, it does provide higher thrust and can work where no oxygen is available in the environment like in space.

I am not sure saying rockets have "higher thrust" make sense. The specific thrust is certainly lower (oxidizer now counts) and the total thrust depends on the engine. The other advantage of rockets, besides being able to operate in space, is that they can operate at hypersonic speeds while turbojets can't and scramjets are still mostly experimental.

It would nearly triple the amount of fuel: 1 kg of fuel plus 1.7 kg of O2 = 2.7kg, almost triple the original 1kg!

Isn't O2 kind of a pain to carry, too? Wouldn't it either occupy a large volume or require either very high pressure or cryogenic storage? Rockets tend to opt for the latter solution, as far as I know.

No.
As Ratchet freak has already mentioned, carrying oxygen would weigh an aircraft down.
As Peter has mentioned, a jet engine pumps air and burns some of the oxygen, not the full 21% available. Often it burns less than half of the available oxygen.
The reason for this is that the "adiabatic" (that means, assuming no heat transfer) flame temperature for complete combustion of all the oxygen in air is about 2000C. Add to that the fact that the compressor can preheat the incoming air up to 500C in some cases, and you would be looking at a temperature at the exit of the combustion chamber of 2500C.
A jet engine that could use all the oxygen in the incoming air would be more efficient, in accordance with the principles of the Carnot cycle, but unless built of "unobtanium" it would melt and fall apart.
A jet engine needs a turbine to do two things. The first is to drive its own compressor. The second is to drive a load (either a propellor or fan.) The turbine+prop/fan is needed because the exit velocity of the exhaust gases would be too high to be used efficiently for generating thrust. Hence putting a turbine in the exhaust path is unavoidable
A rocket has no turbine in the exhaust path, and as a result can run at the extremely high temperatures generated by burning oxygen. It also has extremely high exhaust exit velocities, which are hopelessly inefficient at the kind of vehicle velocities required for general aviation, but are excellent for space travel, where the more energy you can impart to each ton of propellant, the less propellant you have to carry. Also most rockets to date have been single use, unlike jet engines.
So we are stuck with jet engines which are unable to use all the oxygen in the fuel, due to materials issues. One way of boosting the power of a jet engine (but not the efficiency) is to use an afterburner. This is effectively a second combustion chamber, behind the turbine, where more fuel can be burnt. This creates a huge amount more energy, but comparatively little extra thrust. Remember kinetic energy=0.5mv^2 while momentum=mv. You need to match the exhaust velocity to the vehicle velocity for efficient thrust generation, and an afterburner does not do this, as its purpose is not efficiency, just a quick and dirty power boost.
There are some designs on the drawing board for the very large gas turbines in power stations, where the gas from the turbine, having been cooled by expansion, is sent to a second combustion chamber and then through a second turbine, to enable a higher average heat-addition temperature and improve efficiency. However the benefits are small and as far as I know it has not been tried yet. I suspect it will always be too complex for aviation.
More viable than oxygen would be water injection. Water/steam is now being used for cooling of industrial gas turbines, which reduces the amount of air that must be pumped by the compressor, improving efficiency. However, you would still have to carry it.  Another option (also borrowed from industrial gas turbines) would be to put a heat exchanger in the exhaust gas flow, in order to generate steam for a steam-turbine driven propellor or fan. However, I don't expect to see these tried until all the oil in the world has nearly run out!

I find afterburners to be such a disappointment!

Are expansion turbines in power generation stations really only "experimental"? I would have expected that in fixed generation plants such things would be common. In an aircraft, the extra weight of expansion stages would likely increase the amount of mechanical energy required to overcome drag more than it would increase the amount of energy extracted per unit of fuel, but in a fixed plant that would not be an issue.

@Supercat my experience (industrial, not aviation) is from the heat recovery steam generator side (and more in industrial sizes of tens of MW rather than 100's of MW, but I did get seconded to the utility part of my company for one project.) When you say "expansion turbines" I'm not sure if we've understood each other. Multi-shaft gas turbines are common but not universal. What I was saying is that to have compressor - combustion chamber - turbine - 2nd combustion chamber - 2nd turbine in the flue gas path appeared in a brochure (I believe by GE) and was novel to my colleagues in Utilities

@supercat Adding more rows of turbine blades gives diminishing returns, as the last row back-pressures the preceding ones. Most industrial installations now have a steam generator on the turbine exhaust, to boost overall system efficiency. It extracts heat from turbine exhaust gases while putting very little back pressure on the turbine. A 2nd burner may be employed between the gas turbine and the steam generator. This further improves system efficiency when the steam is used for cogeneration, but not when it's used for electric generation, as you have to consider losses in the steam cycle.

@steveverrill: I'm familiar with the fact that adding rows of blades yields diminishing returns; I would expect the point where they cease to be worthwhile to be different in a plane than in a fixed installation. I'd missed the distinction that there's a combustion chamber between turbine assemblies.

@steveverrill: You need to match exhaust pressure to ambient pressure in an afterburner, not velocities. Matching velocities would result in zero thrust.

Basically, reaction engines are more energy efficient the larger the amount of propellant in relation to fuel is. With a jet engine the propellant is air which happens to already contain more oxygen than is needed to burn the fuel. In theory this might change for a very fast aircraft requiring very fast exhaust velocity, but the engine design would have to change too much for it to be relevant to the question.
The general benefit from more efficient burning (barring some specific performance requirement) would also be better fuel efficiency. Getting better fuel efficiency at the expense of carrying additional oxygen is unlikely to be useful.
I actually toyed with a concept for an engine similar to your idea, but, as mentioned by others, an engine that carries its own oxidizer is basically a rocket, so my concept was really a rocket-powered-bladeless-fan with characteristics similar to jet engines not an actual jet engine. So even approaching it from the opposite direction the answer is "The design would have to change too much."
People have actually tested engines based on using conflagration or detonation instead of combustion for more efficient burning of fuel. See Pulse Detonation Engine for example. These still fall in the category of "The design would have to change too much." Also note that they have not replaced jet engines despite the concept having been known for decades. Wikipedia has lots of articles on rare or experimental engines. You might find something close to your idea there.


text:
Can a large passenger aircraft recover from a stall?
In fighter aircraft, we know that they have good enough of maneuverability. But in case of a passenger airplane, if a stall happens is the aircraft maneuverable enough to recover from it?

This question may be related, although it's about spins, not stalls

Manoeuvrability normally means how sharp turn an aircraft can make and how quickly it can roll into and out of it. Stall and spin recoveries are rather independent of that.

I think this may be off-topic because the basis of your question is flawed: maneuverability and stall recoverability are not normally linked.

@CGCampbell Well, not directly, but they are somewhat correlated... negatively. :) I don't think the question of whether an airliner can be recovered from a stall is off-topic, though. Also, stall recovery does usually involve a maneuver (though it's a pretty trivial one,) so the question isn't entirely incorrect, though it does use 'maneuverability' contrary to its normal meaning within aviation.

@CGCampbell Also, I'm not sure that a false premise in a question actually makes it off-topic. It's not unusual for someone not familiar with a field to have false assumptions about it (or even for someone familiar with a field to have false assumptions about some more obscure parts of it.) The underlying question - whether an airliner can be recovered from a stall - is perfectly answerable and on-topic - and has been answered.

The main thing that is required for a stall recovery is just the ability to drop the nose to decrease angle-of-attack and regain airspeed (and, of course, adding power helps, too.) Except in the case of deep stall, there is still sufficient air flowing over the horizontal stabilizers (and, thus, the elevators) in an airliner to push the nose down during a stall. Furthermore, most airplanes (including nearly all, if not all, airliners) are designed with a center of gravity forward of the center of lift. In normal flight, the air flow over the horizontal stabilizers actually pushes the back of the plane down, which holds up the nose. During a stall, this airflow is reduced (still present, but to a lesser degree,) which will cause the nose to tend to drop by default during a stall condition, even if the pilot (or autopilot) gives no additional control inputs at all. As such, normal (e.g. not fighters or aerobatic planes) will recover from a stall on their own with no additional control inputs, given enough altitude.
As already mentioned, some altitude is also usually required for successful stall recovery. This is because the recovery procedures involve dropping the nose which will briefly result in some descent. The lack of sufficient altitude to recover was the main problem in Asiana 214, which crashed just short of the runway in San Francisco. The aircraft was already too low and too slow to recover before the pilots acted. If I remember correctly, they started attempting a go-around only about 7 seconds before the aircraft impacted the seawall. At that point, there was nothing they could do. A small, piston-engine aircraft probably still could have recovered from that situation because piston engines spin up much, much faster than jet engines and could provide the power needed to recover much faster. Pushing the nose down alone would still technically have recovered the plane from the stall condition in this case, but that wouldn't have been very helpful, since it would have meant a nose-first impact into either San Francisco Bay or the seawall, which would obviously have been a much worse outcome.
Another problem that can happen (though is very, very unlikely on an actual airline flight, but much more likely on cargo flights in airliners) is for the cargo to shift to the point that the center of gravity is too far from where it's designed to be for stall recovery to be possible. This is what happened on National Airlines Flight 102, a 747 cargo flight departing from Bagram Air Force Base in Afghanistan. Very shortly after takeoff, the cargo shifted to the back of the aircraft, preventing the pilots from being able to lower the nose enough to keep the plane from stalling. It stalled and crashed before ever leaving the property of the airfield.
In general, pitch stability (more precisely known as longitudinal static stability) is what makes an aircraft capable of stall recovery, not maneuverability. While it may seem counter-intuitive to those not familiar with aerodynamics, it's likely actually easier to recover from a stall in an airliner than it is in a fighter (and almost certainly easier to recover in, say, a Piper or Cessna than a jet fighter.) This is because more maneuverable aircraft (such as fighters and aerobatics aircraft) are usually less stable than less maneuverable aircraft like airliners and normal GA aircraft.
The answers to this question give a thorough explanation of stall recovery which I would recommend reading. Its answers apply to how stall recovery is performed in any normal airplane, not just airliners. That question isn't specifically about whether airliners can recover from a stall, though, which is why I didn't mark this one as a duplicate.

An airliner certainly has the ability to recover from a stall, given sufficient height and power. Moreover stall recovery isn't about maneuverability as such. A fighter jet is more difficult to recover from a stall than a Cessna 150, but the Cessna is much less maneuverable. (That is one among many reasons people learn to fly on Cessna 150s and not on fighter jets.)
It's also not a given that a fighter jet is easier to recover from a stall than an airliner.

Well, that and the fact that a Cessna costs around 300K while a fighter jet is at least 30M.

@Octopus And that's the new price. The used planes that a lot of people actually train in (myself included) can be more like $20-$30k.

Yes and no.
If a stall happens while the plane is low to the ground without sufficient power to maintain altitude, there may not be time to recover.
At altitude, there is plenty of time for a plane to recover from a simple stall, and yes the plane has the maneuverability to do so.
Other conditions, like severe icing, may render the plane unable to recover.
All this assumes a plane without mechanical problems.  Air France flight 447 had airspeed sensor problems and the pilots were presented with confusing information, they stalled the plane at altitude and rode it down into the ocean.  All aboard perished.

Can a large passenger aircraft recover from a stall?

Yes
Airbus stall training video

Here's what Boeing & Airbus say

this article was written jointly by Airbus, Boeing Commercial Airplane Group, and Douglas Products Division. The article focuses on Airbus and Boeing airplanes that do not have electronic flight controls, commonly known as fly-by-wire. However, when a fly-by-wire airplane is in a degraded control law (mode), the recovery techniques are appropriate.
...
An airplane stall is characterized by any one (or a combination) of the following conditions:

Buffeting.
Lack of pitch authority.
Lack of roll control.
Inability to arrest descent rate.

These conditions are usually accompanied by a continuous stall warning. A stall must not be confused with the stall warning that alerts the pilot to an approaching stall. Recovery from an approach to stall is not the same as a recovery from an actual stall. An approach to stall is a controlled flight maneuver; a stall is an out-of-control, but recoverable, condition.
...
STALL RECOVERY.
In all upset situations, it is necessary to recover from a stall before applying any other recovery actions. To recover from the stall, angle of attack must be reduced below the stalling angle. Nose-down pitch control must be applied and maintained until the wings are unstalled. Under certain conditions, on airplanes with underwing-mounted engines, it may be necessary to reduce some thrust in order to prevent the angle of attack from continuing to increase. Once unstalled, upset recovery actions may be taken and thrust reapplied as needed.

(my emphasis).

A Bloomberg article: Does Your Airline Pilot Know How to Escape From a Stall? says

When planes do crash, the No. 1 cause is pilot loss of control. From 2001 to 2010, 1,756 people died in 20 such disasters. About half of these accidents involved aerodynamic stall,

Although this article suggests more training of pilots in stall recovery, the emphasis is properly on preventing a stall.

The Air France tragedy was partly that according to the flight data/voice, and some other impingent facts of note.  Very high altitude, near the limit of the type for both altitude and air speed (actual air speed ~ 250 kts !!), also due to high air temp, less power, and non-stall velocity/AOA envelope was then very small.  The pilot at the controls saw (typical for equatorial mid atlantic nights) severe weather ahead, and wanted to get on top of it.  He really wanted altitude. Then the pitots iced, and he was suddenly a fish out of water, and he started to try to climb more, putting it into a stall regime, but he didn't seem to realize.  They got into worse shape (up to 45 deg bank excursions) and the Captain was awakened and came to the flight deck, but apparently never touched a control. in just a short time, the ice cleared, the pitots were good. the plane that hit the water was a 100% functional machine. Then the problem seemed to be language - although all French, when co pilot suggested he get "more" he meant airspeed, but didn't say put the nose down. The first pilot continued to try to put the nose up ("more altitude". those two pilots went back and forth, verbally and override=preempting control of the control system from each other. Mean while, the flight deck annunciator for "STALL" had shut it self off after a while cuz it was given an "impossible" angle of attack as input, and gave up.  It was so far nose up, the software disregarded it as a broken signal.  Speculation is this reinforced the "climbing" pilots conclusions. This all went on as it plowed thru the air for several minutes, from +40K ft to the predicted last chance at 13Kft, when in theory, they could have still gotten the nose down enough for lift velocity then pull up before the wave tops that killed them. They never began a real stall recovery (other than to NOT roll over into an inverted dive or spin).  They continued to argue and be confused, and unmanaged.
My source for all of this was a good, detailed treatment in VOGUE, a few months ago.
The plane most certainly could have been flown home, but not in boxes and bags, as it was.
It was capable of recovering, given the most altitude any pilot might ever get to start an emergency.  I sit next to a SW developer from the 777 project (did flap control), and he was bemoaning the fact ...yes, Airbus went too far in expecting lesser trained crews to save the plane via auto systems, vs the perception that Boeing style designs were more likely to let a good pilot know what the plane is doing, and not doing, and get on with flying it.

This answer seems to focus on the story of the Air France accident instead of the question (over 70% screen space).

This would be a good answer to "what happened to AF447 in 2009?" but it doesn't directly address the question above. Since AF is large and long established there have inevitably been several "AF tragedies" (AF4590 in 2000 is also notable) - it would be better to identify the specific event at the start. Also, wall-of-text: paragraphs aid reading. P.S the official report might be a better reference than Vogue magazine. Some edits to this answer could make it a higher scoring answer.

It depends on the aircraft type. For instance, Tu-154 cannot recover from stall unless a special stall-recovery parachute is installed in its tail. The parachute normally is only installed during development testing, and never on the regular airlines.

That's interesting. Can you provide a link for a source on that? The wiki article doesn't seem to contain anything about either the inability to recover from a stall or the parachute. I'm curious why it would be unable to recover from a stall. Is its design aerodynamically unstable? That would be very unusual for an airliner.

@reirab there are several reasons. First, its tail is overloaded because of 4 engines (3 main and 1 aux) inside. There is no way to lower the nose after stall. Second, the wings shadow out the engines and the elevator at high attack angle making encreasing engine power and elevator useless. Third, at high attack angles the turbulent air from wings reaches the engines often triggering surging, and at even higher angles air hunger in the engines (due to wing shadowing) starts, making increasing power impossible. Engines just go off. The parachute is meant to rise the tail to reduce the angle.

That sounds like a deep stall. Is it possible to stall a Tu-154 without entering deep stall? If so, would such a stall be recoverable by normal means? Also, it would probably be good to add that information to your answer rather than just having it in the comments. A source would be great for those of us interested in further reading, too, if you can find one.

@reirab from deep stall Tu-154 cannot recover even with a parashute... Stall longer than 2-3 sec means certain death for a regular liner.

Yes an airliner can recover from a stall. The question of the pilots abilities to recover from that stall come into play.
Most modern airliners (Boeing, Airbus, Candair) install "stick shakers/ stick pushers," which are designed to alert the pilot to a stall and attempt a recover from the stall before it happens. If the pilot were to push the airliner into a stall, there is a possibility that the jet would not recover "nose down" as previously stated because of the aerodynamics of an airliner. This requires a stalled horizontal tail surface as well; a highly unlikely situation.
In this case, if a tail-down command occurred, the pilot would need to press full deflection on the ailerons, possibly supported by spoilers, to either side to bring the aircraft over.
Pushing forward in a stall situation would result in one of two scenarios:

the airflow over the horizontal stabilizers would not be sufficient to bring the nose down and the stall would continue,
the tail gets lifted, the angle of attack decreases and the airplane recovers.

So with the aileron at full deflection the aircraft would roll and bring the nose down, and once level or below the horizon the pilot could then begin to gain airspeed and roll the aircraft out of the high roll angle and begin a normal stall recovery with positive G-forces.
Edit: According to Boeing, my previous comment is not totally supported. This answer is based on a "nose high, wings level" situation. Per Boeings website, they state-
"If normal pitch control inputs do not stop an increasing pitch rate, rolling the airplane to a bank angle that starts the nose down should work. Bank angles of about 45 degrees, up to a maximum of 60 degrees, could be needed. Unloading the wing by maintaining continuous nose-down elevator pressure will keep the wing angle of attack as low as possible, making the normal roll controls as effective as possible. With airspeed as low as stick shaker onset, normal roll controls -- up to full deflection of ailerons and spoilers -- may be used. The rolling maneuver changes the pitch rate into a turning maneuver, allowing the pitch to decrease. Finally, if normal pitch control then roll control is ineffective, careful rudder input in the direction of the desired roll may be required to induce a rolling maneuver for recovery.
Only a small amount of rudder is needed. Too much rudder applied too quickly or held too long may result in loss of lateral and directional control. Because of the low energy condition, pilots should exercise caution when applying rudder."
Hopefully this is the support that was asked for. I personally came across the aforementioned answer during aerodynamics class in college.

Hello Flyboy128, welcome to Aviation.SE.

You're right about the presence of the stick shakers. As far as your statements about the aerodynamics of an airliner, do you have any sources to back that up? It would be especially nice to have a source for your second scenario. Dropping a wing is certainly a way to get out of a stall, but dropping the nose is usually the recommended way when it's possible. In most airplanes (including most airliners,) the nose will drop on its own in a stall, due to decreased effectiveness of the horizontal stabilizers. The primary exception to this is a deep stall.

@reirab: I edited the obvious nonsense out of the answer.

Your premise is flawed. It is easier to recover from a stall in a passenger jet than in a fighter jet. An airliner (glide ratio 15:1) is much more buoyant than a fighter (glide ratio 8:1). When a fighter stalls, it drops like a brick and pray it is not in a bad attitude when that happens.

This is totally wrong.

Ease of stall recovery is determined mainly by stability, and to a lesser extent by design features (eg. T-tail vs. conventional tail).  Glide ratio is almost entirely irrelevant.

LOL Anixx, what are you even doing on this site? Are you like stalking me? As for Mark's comment, while that is true, can you name a better metric for stability?

Stalls occur more frequently than you may think. A stall is basically when there is no lift being generated due to lack of air moving past the wing. In fact, when an airliner takes a somewhat steep turn, the outer edge of the wing starts stalling before the inner tip of the wing due to a slight tilt in the airliners wings, called a wash-in wash-out. This way, the pilot still has some control of the aircraft in order to correct it. So yes, the answer is that an airliner can indeed recover from a stall. In situations where the stall angle is too high and the speed is too low, the airplane may not be able to recover, as it most likely would be falling down like a rock, but majority of the time, given enough altitude and speed, it is possible to correct the stall. There have been many cases where pilots have recovered from stalls without crashing.


text:
What accident or safety data is available for ultralight aircraft?
Is there any source of reliable accident or safety data available on ultralight vehicles (FAA Part 103 or similar)?
I'm interested in comparing them to other aircraft types.

Did you search through the NTSB Accident Database? One aircraft category you can choose from is "Ultralight", and then you can further narrow it down if you wish.

As the NTSB, The french BEA also publish reports for ultralight (e.g. this one)

@RonBeyer Assuming I am looking at how safe they are built and not necessarily how well the pilot's can fly wouldn't the data be biased slightly because ultralights require no license to fly?

There aren't that many reports, you could always look for things like structural failure, engine failure, etc in the reports and narrow it down like that.

This could match your need albeit this is a study from the Finnish Accident Investigation Board, based mostly on Finland numbers over 20 years:

Ultralight Aviation Safety and its Improvement through Accident Investigation (151 pages).

Chapter 9, page 87, also introduces information about other countries related to what they do regarding investigation: Croatia, Cyprus, Denmark, Georgia, Germany, Hungary, Iceland, Ireland, the Netherlands, Norway, Portugal, Spain, Sweden and the United Kingdom.
There is a comparison between ultralights and other types likes gliders and GA aircraft:

Source: Accident Investigation Board
Interestingly, while accidents are decreasing in Finland, this is the opposite trend in France (French article from UL federation, based on insurance notifications, from 15 fatalities in 2006 to 30 in 2010). Maybe just a matter of pilots number increasing.
Related:

Microlight/Ultralight Accident Statistics - Adventure/sport/aircraft: France, Germany, UK, Australia, Canada. From this document: "There is no good accident data for ultralights in the US".
Aviation statistics, including ultralights (1998–2007) Canada, TSB.
British Microlight Accident Analysis, many criteria (MS Word).
Recreational aviation risk survey -  Finnish
Transport Safety Agency.

This is great!  Do you know off hand if the ultralights require a license in any of those states?  Part of the issue is that if there is higher requirements in one state over another it is quite likely that those are altering the crash statistics.

See 5.1 Ultralight Pilot Licence requirements for Finland. For the other respondends to the survey, it's not said, but I think that if they have a licence requirement, then they investigate accidents, this information is available from the survey. The Finnish report take this element into account in its analysis (from what I've seen by reading very quickly).

authors: เสฐียรพงษ์ บัวสถิตย์


text:
What's the reasoning for safety wire on aircraft, and the reasoning behind the way it's routed?
I'm assuming saftey wire is used near propeller assemblies where a lot of vibration occurs, or where the different speeds and altitudes aircraft are at could cause expansion or contraction based on temperature.  Is that correct?
I'm also wondering the reasoning for routing them in this manner. Is it done this way to counter vibration so both bolts don't loosen? If one is going counter-clockwise due to vibration, I'm assuming it'd be tightening the other bolt or vice versa?

Related question

"I'm also wondering the reasoning for routing them in this manner." What other way would you route them? Right now, it's routed so as to pull both bolts tighter. You could route them so as to tighten one and loosen the other, or to loosen both, but that doesn't sound like an improvement.

Safety wire (positive wire locking) is done in areas where there is a possibility of the bolt getting loose due to vibration (also in other critical areas); this is done in a way such that the loosening of the bolt is counteracted by the tension in the wire i.e. in case the bolts loosen, the locking wire becomes taut and prevents further movement of the bolt.

safety wire examples; image from www.stangtv.com
There are different ways of doing wire locking for locking depending on the number of fasteners involved, but the basics are the same.

Safety wires; image from FAA AC 43.13-1B - Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair

The text of this answer only mentions bolts. It is worth noting that safety wire is also commonly used to secure nuts and other hardware.

@JonathanWalters Also oil filters. Stupid oil filters....

@voretaq7 Yes, very true. But you know you could just get rid of the oil filter and go back to the oil strainer. The O-320 does superbly with the old style oil strainer and requires no replacement of the safety wire when reinstalling after cleaning (just a new gasket and four new lock washers).

The screen on my O-360 requires safety wire, because Lycoming hates you and wants you to be miserable. (It's also buried, because you're not having fun if you're not bending your arm in 6 different directions trying to get to the back of the stupid engine, which is why it only gets looked at during the annual.)

Air Force we safety wired everything that had the openings for the wire. If we could we would have safety wired the paint on. Jet aircraft also wore safety wire,
The joke was everything had safety wire so the accident inspectors could find all parts and put the aircraft back together! The real reason was to keep nuts and bolts from backing off and disengaging rendering the repair useless. All moving parts had to be safety wired if a part had four bolts or nuts and bolts not only were the bolts and nuts wired but the part itself got wired.

Please consider editing and polishing your answer. As it stands now it is a bit difficult to read.

Welcome! Sounds like you had a lot of experience applying safety wire. If you could add details on why it was routed the way it was, that would help answer the question.

Safety wire is used to keep parts from vibrating apart, it also keeps nuts and bolts from loosening from take offs and landings as well as turbulence in the air. Some parts on aircraft create vibrations on their own when the function. (Like hydraulic pumps) it also keeps lines from slipping off!


text:
Cross a barrier with a drone
How fast does a multi-copter drone need to fly in order to freefall on the other side of a highway if:

Drone weight - 15kg, 20kg
Highway width - 70 ft
altitude above ground - 200 ft, 300 ft, not determined

Thanks!

This looks like homework with no attempt at a solution.

And if it's unpowered, neglecting friction, then it's not really an aviation question as it doesn't matter if it's a drone or a cannonball, it's a basic projectile physics question.

@Transistor homework or research for a smuggling project :')

The time for a free falling object to hit the ground can be calculated with the formula

solved for t this is

with a being the acceleration (in this case a = g = 9.81 m/s) and s elevation in meters above ground.
Once you have calculated this time, you can calculate the distance the object travels horizontally during that falling process by simply multiplying horizontal speed of the object in meters per second by the time in seconds.
Notes: These formulas are based on the assumptions that there is no friction (meaning vacuum in this case). This is obviously not perfectly correct and especially airfoil objects will have a massively different behavior depending on the surrounding air, but this is the basic physics.

I am intentionally not providing the final formula here, as it looks like this is some kind of homework and you should solve it on your own. Therefore I mentioned the basics but leave the work of combining and solving formulas to you.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
How to differentiate two flights with the same flight number that arrive on the same day?
I'm currently working on a piece of software that includes flight information. I have access to flight schedules and I'm making each days flight unique based on flight number and the date that it arrives.
I've hit a problem trying to differentiate flights that arrive on the same day though.
Example:

On Sunday, Flight LS1494 leaves at 19:50 and arrives the next day at 00:25.
The next day, on Monday, LS1494 leaves at 16:40 and arrives at 21:15, making it arrive twice in one day.

Is there a standard way to differentiate these? I have one source of data that includes an "Operational Suffix" of "B" for the flight that originally left on Sunday but I'm not sure if that is actually relevant.
I could include the actually arrival time to identify them however sometimes that scheduled time changes and doesn't get updated immediately which can cause problems.

Possible duplicate of: https://aviation.stackexchange.com/questions/14382/how-are-duplicate-call-signs-dealt-with

That question seems more specific to ATC callsigns. My problem is more related to the flight schedule and flight number and how they are handled in advance of the flight actually running (potentially months in advance). If ATC only decide on the day to change the number then I don't think I can handle that in advance

That differs from airline to airline, I know that KL592 JNB-AMS leaves just before midnight. If that flight is delayed than it receives a new flight number. The main reason being that if something happens to the flight, the relatives on the ground know for certain if there loved one is on the flight or not.

From a software engineers point of view, add the date and time to your key to make it unique...

I'm currently facing a more problematic version of the same difficulty using flight records from the USDT - where you have flight legs with the same number departing on the same day - but it's due to errors in the data. So, +1 for commiseration.

I'm making each days flight unique based on flight number and the date that it arrives.<

A standard used by some (most?) airlines is to refer to the flight by the Flight No and by the departure date (you've already discovered the problem with using arrival dates).
So your example flights would be LS1494/<Sunday date> and LS1494/<Monday date>.

To further this, I would think that you would use the scheduled departure date, not the actual departure date, as late evening flight can obviously be delayed past midnight.

When working with flightplan interfaces between different ATC systems, we have usually set the unique identifier for a flight plan to be CALLSIGN + ADEP + ADES + EOBT + EOBD. (Meaning callsign, departure airport ICAO code, destination airport ICAO code, estimated off-block time, estimated off-block date.) For your example with the same callsign, departure and arrival airport, your differentiating attribute would be the time plus date for departure.
BTW, there are some Eurocontrol standards that are freely avaiable, such as OLDI: https://www.eurocontrol.int/publication/eurocontrol-specification-line-data-interchange-oldi, but I couldn't find a definitive answer there immediately.

Using those five elements also deals with "direct" flights, i.e. multiple legs that share a flight number.